Amorphous poly alphaolefins such as amorphous propylene homo and copolymers, are important for their use in diverse products. The broad utility of these materials is due in large part to the unique combination of chemical and physical properties such as chemical inertness, softness, flexibility, etc., exhibited by these materials.
Conventionally, amorphous polyolefins are mixed with water to deactivate the catalysts and remove unreacted monomer(s). Removing the catalysts and monomer(s) renders wet, tenaciously sticky, granular chunks of the product. For the material to be shaped into various products, the chunks must be dried and then extruded or otherwise shaped.
Extrusion of the material typically involves feeding the dried chunks of the desired polymer from a hopper to the feed section of a screw-type extruder. The polyolefin material is moved through the extruder by screw flights where it is heated and mechanically worked before it is pelletized or otherwise shaped under high pressure. Alternatively, such materials are also shaped by other high temperature methods such as injection molding, roll milling and compression molding. Both lower and higher molecular weight amorphous poly alphaolefins are typically processed as outlined above.
However, existing methods of product transport and recovery require the introduction of water to carry the material through the several stages of recovery from the polymer reactor to the extruder. The extensive use of water by these methods requires that additional storage tanks, delivery and removal lines, and other miscellaneous equipment be used to introduce, maintain, remove and recycle the necessary volume of water. Additionally, existing methods store the material in a chunk form prior to extrusion into useable products, thus requiring additional storage and transport equipment along with the associated maintenance equipment for this intermediate stage of processing. Thus, a need has arisen for a product recovery method and apparatus for recovery of polyolefins, particularly high molecular weight amorphous poly alphaolefins, wherein the use of water during the product recovery is significantly decreased and wherein the intermediate stage of storing and drying the chunk form of the polyolefin is eliminated to enhance production efficiency.
Conventional processing equipment, such as sigma mixers, kneaders or kneader/extruders, are generally known. This conventional equipment is typically used for batch mixing of various materials. High molecular weight amorphous poly alphaolefins exhibit increased tackiness and viscosity, as well as relatively higher softening temperatures, when compared with conventional lower molecular weight poly alphaolefins. This combination of properties makes these higher molecular weight polyolefins a unique processing problem. For example, using conventional handling and transport technologies, high molecular weight amorphous poly alphaolefins tend to plug or clog screws, blades, nozzles, fittings, valves, and piping. This is a particularly troublesome problem for autonomous processing of such materials.
There is also a frequent need to measure the amount of material in a vessel, tank, or other processing or storage facility, all of which are hereinafter referred to as "vessels." It is typically desired that the inventory of the vessels not overflow the available volume, and it is typically also desired that the vessels not become completely empty. These problems can be avoided by measurement of the existing inventory of the vessels to permit more control over the input into and output from the vessels of materials. Each type of vessel, along with various equipment of varying volume inside the vessel, presents a unique challenge in measurement of its inventory.
Conventional inventory measuring means include the following possibilities and attendant problems. One method involves mechanically or electronically weighing the vessels before and after inventory is added, which has the dual problems of poor precision when the vessel weighs much more than the inventory, as well as the requirement that the vessel be movable thereby necessitating use of flexible connections.
Another conventional method for vessels with liquid inventory involves use of a pressure measuring device to determine the hydrostatic pressure in the vessel, but this method is of minimal use when the inventory is a solid or sticky material. Another method involves measuring the increased attenuation of a high energy radiation beam, such as gamma radiation, as it passes through additional mass, but this faces the same precision problems as the weighing method. Another conventional method involves measurement of the surface level by means such as floats, mechanical paddle wheels, electrical probes, ultrasonic transceivers, etc. Each has its own problems, especially when the material may not be evenly distributed throughout the vessel.
None of the conventional methods of measuring the inventory of a vessel are sufficiently accurate for measuring the amount of sticky, high molecular weight amorphous poly alphaolefins of the present invention for the reasons presented above. Thus, there is a need to determine the inventory of such materials in continuous processing equipment to overcome the limitations of conventional weighing technology.